1. Field of the Invention
The present invention relates to wires for semiconductor devices, and in particular to a method of fabricating wires for semiconductor devices suitable for a multi-layers wires constitution.
2. Description of the Background Art
A conventional method of fabricating wires for semiconductor devices will now be explained with reference to FIGS. 1a to 1h. 
Referring to FIG. 1a, an oxide film is deposited on a semiconductor substrate 100 as a first insulation film 101. A titanium nitride (TiN) film is deposited on the first insulation film 101 as a glue layer 102. A tungsten film (W) which is a first conductive layer 103 is deposited on the glue layer 102.
Thereafter, a photoresist film pattern (not shown) is formed on the first conductive layer 103. The first conductive layer 103 and the glue layer 102 are etched by using the photoresist film pattern as a mask, and thus a first conductive layer pattern 103a is formed on the first insulation film 101, as illustrated in FIG. 1b. The first conductive pattern 103a is hereinafter referred to as lower wires 103a. The glue layer 102 formed under the first conductive layer is also patterned, and thus becomes a glue layer pattern 102a. 
Referring to FIG. 1c, a silicon oxide film is formed at the upper portions of the lower wires 103a and the first insulation film 101 as a second insulation film. A photoresist film pattern 105 is formed at the upper portion of the second insulation film. The photoresist film pattern 105 has an opening 106 at a predetermined portion on the lower wires 103a. 
As illustrated in FIG. 1d, the second insulation film 104 is selectively etched by a reactive ion etching (RIE) by using the photoresist film pattern 105 as a mask, thus forming a contact hole 107 or via hole 107 at a predetermined portion on the lower wires 103a. 
As integration of the semiconductor devices is increased, the contact hole or via hole 107 is decreased in diameter (D). Recently, the contact hole is formed to have a diameter equal to or less than 0.2 xcexcm. In addition, the improved integration of the semiconductor devices makes a height (h) of the contact hole or via hole 107 increased. As a result, an aspect ratio of the contact hole is increased, thus causing many problems in a process of fabricating wires in the semiconductor device.
The semiconductor substrate 100 illustrated in FIG. 1d is transferred to a device for depositing a metal film. As shown in FIG. 1e, while the semiconductor substrate 100 is transferred, a natural oxide film 108 is formed on an entire structure of the semiconductor substrate 100.
A precleaning process is carried out on the semiconductor substrate 100 as shown in FIG. 1e in order to remove the natural oxide film 108. As the precleaning process, there are used a wet etching of dipping and rinsing the semiconductor substrate in an HF solution or a sputtering method using an argon (AR) gas. When the AR sputtering method is employed, process conditions are as follows.
Pressure in chamber: approximately 2 mTorr
Source power for generating a plasma: 400 W(13.56 MHz)
Bias power: 270 W(400 KHz)
Process time: 10 seconds
Ar gas flowing amount: 10 cc/min
Thereafter, referring to FIG. 1f, a titanium (Ti) film or a titanium nitride (TiN) film is formed as an adhesion layer or a glue layer 109 on the entire structure of the semiconductor substrate 100 where the natural oxide film 108 is removed, namely at the upper portion of the second insulation film 104 and the inner wall and lower portion of the contact hole or via hole 107. A metal layer, especially a tungsten is not deposited well on the silicon oxide film which composes the second insulation film 103.
Accordingly, the adhesion layer or glue layer 109 is formed so that the metal layer can be firmly adhered at the upper portion of the second insulation film 104 and in the contact hole 107, during a process for forming upper wires, namely a process for depositing a metal layer.
Then, the tungsten film 110 is deposited on the adhesion layer or glue layer 109 by a chemical vapor deposition. The tungsten film 110 is deposited at a sufficient thickness to fill up the contact hole 107, and thus is also formed on the adhesion layer 109 at the upper portion of the second insulation film 110. As shown in FIG. 1g, a chemical mechanical polishing (CMP) or an etchback process is carried out on the tungsten film 110, thereby removing the tungsten film deposited on the second insulation film 104. As a result, a tungsten plug 110a is formed in the contact hole 107.
Referring to FIG. 1h, a metal film is formed as a conductive layer on the entire structure in FIG. 1f, and patterned, thus forming the upper wires 111.
In accordance with the conventional method of fabricating the wires for the semiconductor devices, the tungsten is not deposited well on the insulation film, especially on the oxide film. Therefore, it is required to form the glue layer or adhesion layer on the second insulation film and at the inner walls of the contact hole before forming the tungsten plug.
In addition, after the blanket tungsten film is formed on the entire structure of the semiconductor substrate in order to form the tungsten plug, while the tungsten film at the upper portion of the insulation film is removed by the etchback or CMP process, a number of particles are generated, and thus a fabricating rate of the semiconductor device is reduced.
Besides, the etchback or CMP process is further included, as compared with the process of selectively filling the tungsten in the contact hole. Accordingly, the fabricating process of the semiconductor device is more complicated.
As shown in FIG. 2, in case of a contact hole 200 having a high aspect ratio, a step coverage of the adhesion layer 201 is inferior at the lower portion of the contact hole 200, and as a result the tungsten film is not deposited well thereon. After the tungsten plug 202 is formed, a void 203 is formed at the lower portion of the contact hole 200, and thus a contact between the tungsten plug 202 and the lower wires 204 is inferior, and a contact resistance is increased.
When the adhesion layer is formed thicker in order to improve its step coverage at the lower portion of the contact hole, an overhang takes place at the edge portions of the entrance of the contact hole, and thus a keyhole is generated at the lower portion of the contact hole after deposition of the tungsten film, thereby increasing a wires resistance.
It is therefore a primary object of the present invention to provide a method of fabricating wires for semiconductor devices having a low wires resistance and a low contact resistance.
It is another object of the present invention to provide a method of fabricating wires for semiconductor devices which can reduce a wires resistance and a contact resistance merely by changing conditions of a precleaning process carried out when fabricating the wires for the semiconductor devices.
It is still another object of the present invention to provide a method of fabricating wires for semiconductor devices which can increase a fabricating rate of the semiconductor devices by omitting an etchback process and preventing generation of particles, and which can improve productivity by simplifying a fabricating process.
It is still another object of the present invention to provide a method of fabricating wires for semiconductor devices which can simplify a fabricating process by omitting a process of forming an adhesion layer performed before forming a plug.
In order to achieve the above-described objects of the present invention, there is provided a method of fabricating wires for semiconductor devices including: a step of forming a first insulation film; a step of forming lower wires on the first insulation film; a step of forming a second insulation film on the lower wires; a step of forming a contact hole on the lower wires by selectively etching the second insulation film; a step of performing a precleaning process by using an argon (AR) sputtering method until the lower wires at the lower portion of the contact hole are etched at a predetermined depth; a step of selectively forming a conductive plug in the contact hole; and a step of forming upper wires at the upper portions of the conductive plug and the second insulation film, a re-deposition layer consisting of a material of the lower wires being formed at the inner walls of the contact hole in the precleaning process.
In accordance with the method of fabricating the wires for the semiconductor devices of the present invention, the precleaning process is a step of sputtering for approximately 25 seconds in the conditions of a source power of 500 W, a bias power of 250 W, an argon gas flowing amount of 5 cc/min, and a pressure in a chamber of 0.5 mTorr.